The present invention relates to a gas sensor, and more particularly to a gas sensor for detecting the gas composition of gas exhausted from an engine, for enhancing, for example, the efficiency of a catalytic converter.
Heretofore, an exhaust gas sensor has been proposed which comprises a gas sensing element made of a metal oxide semiconductor such as titanium oxide etc., having an electrical resistance which changes depending on the relative gas environment, and a comparator which connects the gas sensing element in series with a fixed reference resistor. This arrangement converts the resistance of the gas sensing element to a voltage and compares that voltage with a predetermined reference voltage to produce a gas detection signal.
However, in the prior art gas sensor, since the fixed reference resistor is connected in series with the gas sensing element, an error in the gas composition detection may occur. Furthermore gas composition detection may become impossible if the electrical resistance characteristic of the gas sensing element changes with operating temperature or with time.